Balloon dilatation catheters are used in a variety of medical procedures. One such procedure involves percutaneous transluminal angioplasty (PTA) and, particularly, percutaneous transluminal coronary angioplasty (PTCA), in which a balloon is used to dilate an obstructed artery. The PTCA procedure typically involves the use of a very slender, low profile balloon catheter in conjunction with a small diameter steerable guidewire. The guidewire can be manipulated and navigated to and into the coronary arteries to the location of a narrowed arterial portion that is to be dilated with the balloon of the catheter. With the guidewire in place, the catheter then can be advanced over the guidewire to the site of the obstruction. The catheter is advanced to place the balloon within the obstruction and the balloon then is inflated under high pressure to forcibly dilate that region of the artery. The procedure serves to widen the flow passage to permit more effective blood flow through the artery.
Balloon angioplasty catheters typically are used in arteries that are narrow, such as the coronary arteries, and in circumstances where the naturally narrow artery is even further narrowed by the obstruction (stenosis). It is essential, in order to perform the procedure, for the balloon to have a low profile, that is, a small effective deflated cross-sectional diameter so that it can be advanced into the stenosis. To that end, the balloon of the angioplasty catheter typically is formed from a very thin polymeric material that can be wrapped closely about the shaft of the catheter to minimize the profile. Although an undamaged balloon is capable of developing high pressures under inflation, the balloons are delicate and may be susceptible to minor scratches or other damage, as during handling, that could result in premature balloon failure. Consequently, it is a common practice to enclose the balloon portion of the catheter in a sleeve-like balloon protector that is not removed until the catheter is set-up for use by the physician. The balloon protector also may serve to maintain the balloon in its tightly wrapped, low profile configuration during shipment and storage. Examples of some balloon protectors are described in U.S. Pat. Nos. 4,573,470 (Samson), 4,930,341 (Euteneuer), 5,015,231 (Keith), 5,053,007 (Euteneuer), 5,066,298 (Hess), 5,342,307, (Euteneuer), 5,352,236 (Jung), 5,417,707 (Parkola), 5,425,710 (Khair), 5,569,294 (Parkola), and EP 0 744 187 A1 (Klunder).
Another aspect of balloon dilatation catheters, normally unrelated to balloon profile or protection, is that when the catheter is set up for insertion into the patient, the guidewire typically is preloaded into the catheter so that the two can be inserted into the patient's vasculature together. The catheter is provided with a lumen extending longitudinally through which the guidewire is received. The guidewire lumen typically terminates at a distal outlet orifice at the distal tip of the catheter, slightly beyond the distal end of the balloon. After the catheter and guidewire are together inserted into the vasculature, the guidewire then is projected forwardly to the intended site of treatment, as described above, after which the catheter can be advanced over the guidewire to place the balloon at the intended site. The procedure for loading the guidewire into the catheter can present some difficulties. A common technique for loading the guidewire into the guidewire lumen of the catheter is to "backload" the guidewire, that is, to insert the proximal end of the guidewire into the distal outlet orifice at the distal tip of the catheter. The guidewire then is fed proximally through the guidewire lumen until the proximal end of the guidewire emerges from the proximal end of the catheter. Backloading the guidewire into the distal end of the guidewire lumen of the catheter is the only practical way to advance a catheter onto the guidewire that is already in place in the patient, as may occur when the original catheter is to be exchanged with another catheter. The second catheter can only be backloaded onto the proximal end of the guidewire because that is the only end that is accessible outside of the patient. The typically small dimensions of the guidewire, the catheter tip and the distal outlet orifice, coupled with the relatively delicate nature of these components, can present some difficulty in the backloading procedure. By way of example, a guidewire diameter used in PTCA procedures typically can have a diameter of 0.010 to 0.018 inch. The guidewire lumen in the catheter has a diameter slightly greater than the guidewire. The distalmost tip of the catheter shaft, at the distal outlet orifice may be tapered slightly to present an even narrower clearance with the guidewire.
It is among the general objects of the invention to provide a device that serves to protect the balloon while also facilitating backloading of the guidewire into the guidewire lumen of the catheter.